Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive read sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR sensor”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
FIG. 1 illustrates a cross-sectional view of an MR head, in accordance with the prior art. As shown, an MR read head includes an MR sensor which is sandwiched between first and second gap layers G1 and G2 which are in turn sandwiched between first and second shield layers S1 and S2. Lead layers are sandwiched between the first and second gap layers for providing a sense current to the MR sensor. Magnetic fields from a magnetic disk change the resistance of the sensor proportional to the strength of the fields. The change in resistance changes the potential across the MR sensor which is processed by channel circuitry as a readback signal.
An MR read head is typically mounted to a slider which, in turn, is attached to a suspension and actuator of a magnetic disk drive. The slider and edges of the MR sensor and other layers of the read head form an air bearing surface (ABS). When a magnetic disk is rotated by the drive, the slider and one or more heads are supported against the disk by a cushion of air (an “air bearing”) between the disk and the ABS. The air bearing is generated by the rotating disk. The read head then reads magnetic flux signals from the rotating disk.
There are two critical dimensions of the MR head, namely the trackwidth and resolution of the MR head. The capability of the MR head to read data recorded at high areal densities is determined by its trackwidth and its resolution.
The trackwidth of the MR read head is the length of the active or sensing region for the MR sensor and is typically defined by the photolithography and subtractive or additive processing. The trackwidth is defined by the recess generated by the photoresist PR used during a photolithography process.
Resolution, on the other hand, is determined by the gap of the read head which is the distance between the first and second shield layers at the ABS. Accordingly, this distance is the total of the thicknesses of the MR sensor and the first and second gap layers G1 and G2. When the first and second gap layers G1 and G2, which separate the MR sensor from the first and second shield layers S1 and S2, become thinner, the linear resolution of read head becomes higher. A serious limitation on the thinness of the gap layers of the read head is the potential for electrical shorting between the lead layers and the first and second shield layers. The thinner a gap layer, the more likely it is to have one or more pinholes which expose a lead layer to a shield layer. Pinholes can significantly reduce the yield of a production run of MR read heads.
It is important to note that the only place where the gap layers have to be thin is in an MR region where the MR sensor is located. The gap layers can be thicker between the lead layers and the first and second shield layers. Accordingly, it is desirable if each gap layer could be thin in the MR region to provide high linear resolution and thick outside of the MR region to provide good insulation between the lead layers and the shield layers.
The MR read head of FIG. 1 accomplishes this using a two step process of depositing first gap layers before the MR sensor is deposited and a two step process of depositing second gap layers after the MR sensor is deposited. In the present device, a very thin first gap layer G1 is deposited on the first shield layer S1. An MR region is then masked and a first gap pre-fill layer G1P, which may be thicker than G1, is deposited. The mask is removed, leaving the first gap pre-fill layer G1P everywhere except in the MR region. Lead layers L1 and L2 and an MR sensor are then formed.
Next, a very thin second gap layer G2 is deposited. The MR region is then masked and a second gap pre-fill layer G2P is deposited. After lifting off the mask, the G2P layer is located everywhere except in the MR region. The result is that very thin G1 and G2 layers are in the MR region at the bottom and top of the MR sensor to provide the MR head with a high linear resolution, the G1 and G1P layers are located between the leads and the first shield layer S1 to prevent shorting between the lead layers and the first shield layer S1, and the G2 and G2P layers are located between the lead layers and the second shield layer S2 to prevent shorting between the lead layers and the second shield layer S2.
As such, the present device is capable of providing a read head which has a very thin gap layer at the MR region, and yet will prevent shorts between lead layers and the first and second shield layers.
Despite this, the MR read head of FIG. 1 includes gap layers G1, G1P, G2, and G2P which afford many non-planar surfaces in the form of beveled edges circumnavigating the MR sensor. Such non-planar surface must, in turn, be subjected to photoresist layers during processing. Due to inherent limitations of photolithography, two problems result which compromise control of the critical trackwidth and resolution dimensions.
First, the beveled edges cause reflective notching due to light scattering. See arrows in FIG. 1. Secondly, the non-planar surfaces cause non-uniform photoresist coverage during processing which, in turn, invokes the well known “swing curve” effect. FIG. 2 illustrates the manner in which the critical dimensions (trackwidth and resolution) vary as a function of photoresist thickness, in accordance with the swing curve effect. As is well known, the constructive and destructive interference of reflected light within the photoresist film causes the swing curve effect.
Prior art devices have attempted to overcome the foregoing disadvantages through the addition of antireflective layers and planarization. Unfortunately, antireflective layers are only partially effective and introduce complications associated with their removal.
There is therefore a need for an MR read head with an improved gap layer which utilizes planar surfaces to avoid adversely affecting the MR region, while providing a thin gap layer adjacent to the MR region and a thick gap layer between lead layers and the first and second shield layers.